Using CFD to Improve Stall Margin

1999 ◽  
Author(s):  
James R. Hardin ◽  
Charles F. Boal
Keyword(s):  
High Efficiency ◽  
Industrial Applications ◽  
Stable Operation ◽  
Test Results ◽  
Peak Efficiency ◽  
Centrifugal Compressors ◽  
Stall Margin ◽  
Operating Range ◽  
Multi Stage ◽  
Cfd Analyses

Abstract Centrifugal compressors for multi-stage industrial applications must have both high efficiency and stable operation over a wide flow range. CFD analyses were used to evaluate the stall margins of candidate impeller designs compared to a baseline semi-inducer design. With this guidance, a new full-inducer impeller was designed with predicted wider operating range and slightly higher peak efficiency. Prototype tests confirmed these predictions. This paper presents predictions from two CFD codes and test results, for both the original and the redesigned impeller, and discusses the application of CFD for predicting impeller stall.

Stability of Centrifugal Compressors by Applications of Damper Seals

2011 ◽  
Author(s):  
Edmund A. Memmott
Keyword(s):  
Stability Analysis ◽  
Critical Frequency ◽  
Stable Operation ◽  
Test Results ◽  
Case Histories ◽  
Centrifugal Compressors ◽  
Full Load ◽  
Roughened Surface ◽  
Pressure Test ◽  
Full Pressure

This paper surveys the applications of damper seals to provide the stable operation with respect to rotordynamics of centrifugal compressors. Damper seals are applied as sealing devices at the division wall of back-to-back compressors and at the balance piston of in-line compressors. They consist of a roughened surface on the stator that is typically created by a pattern of holes. Rotordynamically stable operation is shown by a lack of or a small bounded amount of SSV (subsynchronous vibration) at the first fundamental lateral critical frequency. Experience plots showing the use of damper seals will be presented. Case histories of the use of damper seals will be given. Stability analysis and full load full pressure test results will be reviewed. The test results show no SSV at the first critical frequency with the damper seals.

An Investigation of the Use of Wet Compression in Industrial Centrifugal Compressors

2006 ◽  
Author(s):  
Ahmed Abdelwahab
Keyword(s):  
Pressure Ratio ◽  
Water Injection ◽  
Centrifugal Compressors ◽  
Power Requirement ◽  
Operating Range ◽  
Multi Stage ◽  
Direct Water Injection ◽  
Compressor Inlet ◽  
Wet Compression ◽  
Compressor Power

Industrial centrifugal compressors generally comprise a number of low pressure ratio intercooled stages. This is done primarily for the purpose of reducing the compressor power requirements and improving the operating range of the multi-stage compressor. In recent years, however, rapid increases in the per-kilowatt-hour prices both domestically and worldwide has led to renewed research efforts to further reduce the power requirements of this type of compression equipment. Several attempts have been made to use direct water injection as a means to overspray the compressor inlet to further reduce its power requirement. This paper presents an investigation into the use of this technology in industrial centrifugal compressors. A simple numerical method is presented for the computation of wet compression processes. The method is based on both droplet evaporation and compressor mean-line calculations. An assessment, based on the developed model, of the effectiveness of evaporative processes in reducing the compressor power consumption per stage is presented. The impacts on stage efficiency and operating range are also presented.

HSCT Forward Swept Fan Performance

2003 ◽  
Author(s):  
Robert J. Neubert ◽  
Charles P. Gendrich
Keyword(s):  
High Speed ◽  
State Of The Art ◽  
Low Noise ◽  
Navier Stokes ◽  
Light Weight ◽  
Test Results ◽  
Flow Solver ◽  
Stall Margin ◽  
Fan Performance ◽  
Multi Stage

Previous experimental and analytical studies have demonstrated the potential for significant improvements in efficiency and stall margin with forward swept rotor blading. This paper extends the assessment to a light weight, low noise two stage fan designed and fabricated under the NASA High Speed Civil Transport program. The experimental investigation evaluates the effect of forward sweep on efficiency and stall margin relative to the predicted levels for a radial fan designed for the same requirements. Efficiency was above multi-stage fan state of the art and stall margin was significantly greater than predicted based on radial fan experience. In addition, the effects of increasing the axial gap between the IGV and rotor 1, as well as R1 to S1 axial gap are evaluated. The increased axial gap between R1 & S1 had a much greater effect on performance than increasing the IGV to R1 gap. And, 3D Navier-Stokes flow solver analysis was performed for comparison to test results.

scholarly journals A Casing Treatment with Axial Grooves for Centrifugal Compressors

2019 ◽  
Vol 4 (3) ◽  
pp. 27 ◽  
Author(s):  
Sebastian Leichtfuß ◽  
Johannes Bühler ◽  
Heinz-Peter Schiffer ◽  
Patrick Peters ◽  
Michael Hanna
Keyword(s):  
Pressure Ratio ◽  
Peak Efficiency ◽  
Centrifugal Compressors ◽  
Reduced Pressure ◽  
Casing Treatment ◽  
Operating Range ◽  
High Pressure Compressor ◽  
Working Principle ◽  
Past Experiences ◽  
Pressure Compressor

This paper provides an investigation of a casing treatment (CT) approach for pressure ratio improvements of centrifugal compressors between peak efficiency and surge. Results were experimentally verified for a variety of automotive turbocharger compressors and analyzed with 3D CFD. The CT design is an adaptation from an axial high-pressure compressor, which was successfully applied and intensively investigated in recent years. The aerodynamic working principle of the applied CT design and the achievable improvements are shown and described. The demand of operating range for automotive applications typically dictates high inlet shroud to outlet radius ratio (high trim) and past experiences indicate that a recirculation zone is formed in the inducer for those centrifugal compressors. This recirculation at the inlet shroud causes losses, a massive blockage and induces a co-rotating swirl at the inlet of the impeller. The result is a reduced pressure ratio, often leading to flat speed lines between the onset of recirculation and surge. This paper provides an understanding of inducer recirculation, its impacts and suggests countermeasures. The CT design for centrifugal compressors only influences flow locally at the inducer and prevents recirculation. It differs substantially in design and functionality from the classical bleed slot system commonly used to increase operating range. An experimental and CFD comparison between these designs is presented. While the classical bleed slot system often provides a massive increase in operating range, it often fails to increase the pressure ratio between onset of inducer recirculation and surge. In contrast, the CT design achieves a gain in pressure ratio near surge.

A Model for System Instability Analysis in a Multi-Stage Intercooled Industrial Compressor

2019 ◽  
Author(s):  
Jiaye Gan ◽  
Ahmed Abdelwahab ◽  
Viktor Kilchyk
Keyword(s):  
Guide Vane ◽  
Transient Behavior ◽  
Industrial Applications ◽  
Operating Conditions ◽  
System Response ◽  
Stable Operation ◽  
System Behavior ◽  
Multi Stage ◽  
Performance Reduction ◽  
Inlet Conditions

Abstract Compression equipment used for industrial applications are typically comprised of multi-stage intercooled compressor stages. The presence of large volume intercoolers between individual stages adds a layer of complexity currently not present in publicly available surge models both in terms of system behavior and recovery analysis. In this work a compressible, temporal, and spatial model is developed in which the conservation equations are solved numerically for each of the system components, i.e. pipes, plenums and heat exchangers, valves, and individual compressor stages. The model can identify the onset of instability on an individual stage basis as well as the switching that can occur between the controlling stages of the instability onset when the operating conditions change, e.g. changes in inlet conditions, intercooler fouling or cooling tower performance reduction, and speed or guide vane changes. The model is therefore used both as a stage stacking model during the compressor stable operation as well as a model of the transient behavior of the system past the stable operation. An inertial model of the compressor drive train is also incorporated to analyze the effects of power transients, e.g. emergency shut down (ESD), on the system behavior. In this article details of the developed model are provided. Several test cases are presented. The model is then used to demonstrate the proper sizing of a vent valve of a base load compressor to meet the required system response specification in a surge event. The developed model represents an improvement over available transient system models in terms of predicting the post stable behavior of multi-stage intercooled compressors.

High Specific Speed, High Inducer Tip Mach Number, Centrifugal Compressor

2003 ◽  
Author(s):  
C. Rodgers
Keyword(s):  
Mach Number ◽  
Centrifugal Compressor ◽  
Transonic Flow ◽  
High Efficiency ◽  
Flow Fields ◽  
Test Results ◽  
Positive Slope ◽  
Stall Margin ◽  
Recovery Characteristic ◽  
Specific Speed

The demand for more efficient turbocharger and aviation centrifugal compressors operating at higher pressure ratios and specific speeds with extended flow ranges is focusing research efforts on the inducer and diffuser transonic flow fields. At pressure ratios above 5.0 and specific speeds of unity inducer tip relative Mach numbers exceeding 1.4 can be encountered, precipitating both increased shock losses and diminished stall margin. The results of compressor rig testing on a research 6.8 inch tip (173mm) diameter single stage centrifugal compressor operating with inducer tip relative Mach number up to 1.5 are presented. The test results reveal high efficiency combined with extended flow range. This was achieved through improved impeller stability with shroud bleed, thereby permitting the diffuser to operate stably on its positive slope recovery characteristic.

scholarly journals Stall Margin Improvement in a Centrifugal Compressor through Inducer Casing Treatment

2016 ◽  
Vol 2016 ◽  
pp. 1-19
Author(s):  
V. V. N. K. Satish Koyyalamudi ◽  
Quamber H. Nagpurwala
Keyword(s):  
Mass Flow ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Treatment Technique ◽  
Centrifugal Compressors ◽  
Stall Margin ◽  
Casing Treatment ◽  
Operating Range ◽  
Stable Operating ◽  
Stall Margin Improvement

The increasing trend of high stage pressure ratio with increased aerodynamic loading has led to reduction in stable operating range of centrifugal compressors with stall and surge initiating at relatively higher mass flow rates. The casing treatment technique of stall control is found to be effective in axial compressors, but very limited research work is published on the application of this technique in centrifugal compressors. Present research was aimed to investigate the effect of casing treatment on the performance and stall margin of a high speed, 4 : 1 pressure ratio centrifugal compressor through numerical simulations using ANSYS CFX software. Three casing treatment configurations were developed and incorporated in the shroud over the inducer of the impeller. The predicted performance of baseline compressor (without casing treatment) was in good agreement with published experimental data. The compressor with different inducer casing treatment geometries showed varying levels of stall margin improvement, up to a maximum of 18%. While the peak efficiency of the compressor with casing treatment dropped by 0.8%–1% compared to the baseline compressor, the choke mass flow rate was improved by 9.5%, thus enhancing the total stable operating range. The inlet configuration of the casing treatment was found to play an important role in stall margin improvement.

scholarly journals The Effects of Lean and Sweep on Transonic Fan Performance

2002 ◽  
Author(s):  
J. D. Denton ◽  
L. Xu
Keyword(s):  
High Efficiency ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Peak Efficiency ◽  
3D Design ◽  
Stall Margin ◽  
Fan Performance ◽  
Transonic Fan ◽  
Shock Loss ◽  
Design Techniques

The aerodynamics of transonic fans is discussed with emphasis on the use of three-dimensional design techniques, such as blade sweep and lean, to improve their performance. In order to study the interaction of these 3D features with the shock pattern a series of five different designs is produced and analysed by CFD. It is found that the 3D features have remarkably little effect on the shock pattern near the tip where the shock must remain perpendicular to the casing. Lower down the blade significant shock sweep, and hence reduced shock loss, can be induced by 3D design but this is usually at the expense of reduced stall margin and increased loss elsewhere along the blade span. Overall, very little change in peak efficiency or pressure ratio is produced by blade sweep or lean. However, there are significant effects on stall margin with forwards sweep producing a better stall margin and maintaining a high efficiency over a wider range.

Experimental Investigation of the Diffuser Vane Clearance Effect in a Centrifugal Compressor Stage With Adjustable Diffuser Geometry: Part II — Detailed Flow Analysis

2014 ◽  
Author(s):  
Stefan Ubben ◽  
Reinhard Niehuis
Keyword(s):  
High Efficiency ◽  
Negative Impact ◽  
Pressure Ratio ◽  
Flow Analysis ◽  
Industrial Applications ◽  
Characteristic Line ◽  
Stall Margin ◽  
Clearance Flow ◽  
Geometry Parameter ◽  
The Impact

The combination of variable speed control and adjustable diffuser vanes offers an attractive design option for centrifugal compressors applied in industrial applications where a wide operating range at high efficiency level and a favorable surge line is required. However, the knowledge about the impact on compressor performance of a diffuser vane clearance between vane and diffuser wall which is mandatory since the diffuser geometry adjustment has to take place during operation, is still not satisfying. The results of characteristic line and probe measurements presented in Part I [18] of this two-part paper showed that an one-sided diffuser clearance not necessarily need to lead to a negative impact on compressor operating behavior but is able to contribute to an increase in flow range, stall margin, pressure ratio and efficiency, as long as the diffuser passage is broad enough with respect to the clearance height. In order to reveal the relevant flow phenomena, in Part II the results of detailed measurements of the pressure distribution at diffuser exit and Particle Image Velocimetry (PIV) measurements inside the diffuser channel performed at three clearance configurations and three diffuser angles at a fixed radial gap are discussed. It was found, that for defined diffuser configurations the clearance flow amplifies the diffuser throat vortex capable to reduce the loading of the highly loaded vane pressure side and to support a more homogenous diffuser flow. It turned out that the coaction of the geometry parameter diffuser vane angle and diffuser clearance height is of particular importance. The experimental results are published as an open CFD testcase “Radiver 2” [17], extending the experimental data base of the testcase “Radiver” published in 2003 by Ziegler [24].

The Klystrode® Iot a New, Compact, High Efficiency Electron Tube

1994 ◽  
Vol 347 ◽  
Author(s):  
R. Donald Peters ◽  
Andrew Haase ◽  
Chris Johnson ◽  
Robert N. Tornoe
Keyword(s):  
High Power ◽  
Field Experience ◽  
High Efficiency ◽  
Industrial Applications ◽  
Test Results ◽  
Electron Tube ◽  
Improve Efficiency ◽  
The Past

ABSTRACTThe Klystrode® (IOT) is a new high power electron tube which combines the features of Klystron and the Tetrode. During the past six years it has virtually taken over the UHF-TV market and has demonstrated its capabilities in high power research applications. This paper describes the principles of Klystrode IOT operation and the power and frequency ranges where it is most useful. Field experience with over fifty (50) transmitters in UHF TV service is reported as well as test results from high power scientific devices operated at 267 MHz, 250 kW (CW) and 425 MHz, 500 kW (pulse). Finally, future improvements in the Klystrode IOT to reduce cost, improve efficiency and optimize the tube for industrial applications.

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